An aeration apparatus and a method of aeration conventionally used in lakes, ponds, fish-and-shellfish breeding ponds, polluted water treatment facilities or the like include a surface-agitation type aeration apparatus using an electric motor to agitate the surface of water with agitation blades as well as an air diffuser, an aeration apparatus and a method of aeration in which gas is released from air diffusing pipes arranged at the bottom thereof to generate bubbles in water, thereby bringing water and gas into contact with each other.
For example, Japanese Patent Application Laid-Open Publication No. 2006-326524 has disclosed an invention of an air diffuser in which, with the aim of improving the efficiency of oxygen dissolution by decreasing bubble diameters to be produced to increase a gas-liquid contact area, a meshed cloth is used on an air-diffusing surface. Further, Japanese Patent Application Laid-Open Publication No. 2004-141730 has disclosed inventions of a method of aeration and an aeration apparatus used in a sewage treatment system in which microbubbles (the diameter of which is 100μ or smaller) are produced in an aeration tank to agitate polluted water.
However, in the above-described conventional air diffusers, aeration apparatuses and methods of aeration described in Publication Nos. 2006-326524 and 2004-141730, a gas dissolution method based on the fact that gas is made smaller in size to increase the contact area of gas with liquid to prolong the contact time of gas with liquid is adopted, thereby posing a problem that oxygen is supplied at an extremely low efficiency. Further, where conventional aeration is repeated in which pressure is applied to air inside a water tank having aquatic organisms, these organisms consume oxygen gas of gas components dissolved in water, thereby the water of the tank is finally changed into that containing a large amount of unnecessary gases such as nitrogen gas and is inferior in gas dissolution balance. In other words, there is a problem that the above method is unable to make water quality in a tank appropriate for aquatic organisms.